Radioactive seed-holding device

ABSTRACT

An apparatus is described that efficiently resupplies radioactive seeds to a brachytherapy applicator. A seed-holding system includes a holder and a transfer device. The holder, which may be disposable, stores the radioactive seeds and the transfer device, which may be reusable, helps shield and dispense the seeds. The holder is coupled to the transfer device, and the apparatus is mated to an applicator. After seeds have been dispensed, the apparatus may be disconnected from the applicator and the empty holder may be ejected from the transfer device, and replaced with a full holder.

This application is a continuation of application of U.S. applicationSer. No. 09/792,307, filed Feb. 23, 2001, now U.S. Pat. No. 6,572,527.

BACKGROUND

This invention relates to medical devices and, more particularly, tomedical devices useful in providing brachytherapy.

Brachytherapy is a form of cancer treatment, in which radiation sourcesplaced inside the patient's body irradiate a tumor. In brachytherapy, asurgeon usually implants several radioactive seeds in or around thetumor, thus providing a higher radiation dose to the tumor than would bepossible with external beam radiation therapy. Careful placement of theradioactive seeds allows localized and precise irradiation of the tumor.Because the radiation dose diminishes rapidly outside the radioactiveseed, the radiation dose to surrounding healthy tissues is reduced.

Radioactive seeds typically are tiny (usually 1 mm by 4.5 mm), roughlycylindrical objects containing very small amounts of radioactivematerial. In one widely practiced brachytherapy procedure, theradioactive seeds are implanted permanently inside the patient's body.The half-life of the radioactive material is generally short, and theradioactivity in the seeds decays after about three to six months to thepoint that there is little detectable radiation. Two radioactiveisotopes commonly used for permanent implants are iodine-125, often usedto treat slower growing tumors, and palladium-103, which is preferredwhen the tumor is fast-growing. Other radioactive materials have beenused in implants as well.

Many forms of cancer respond to brachytherapy, including several formsof prostate cancer. Brachytherapy is generally less invasive thansurgery, usually results in fewer side effects for the patient thansurgery or external beam radiation, allows for a short recovery time andreduces the impact upon the patient's quality of life.

SUMMARY

In brachytherapy treatment, it is common for the physician to implant alarge number of seeds in the patient's tissue. In a typical prostateimplantation, for example, eighty to one hundred twenty radioactiveseeds may be implanted at varying positions in and around the prostate.The physician uses a device called an applicator to perform theimplantation. The applicator usually includes a slender push rod (orstylet) to push the radioactive seeds into a hollow implantation needle.The implantation needle, which is usually coupled to the applicator,penetrates the patient's body and is used to deliver the seeds to thetumor and the area around the tumor. Typically, the surgeon advances aradioactive seed through the needle to a desired location. To delivermultiple seeds, the surgeon can repeatedly place seeds into the voidspace created by retracting the needle. In some brachytherapyprocedures, several implantation needles may be employed, each needlepenetrating the patient at a different site. In such a procedure, asingle applicator may be used for all of the implantations, theapplicator coupled to each needle in turn. In other brachytherapyprocedures, a single applicator and a single needle may be used forimplantations at several sites.

Usually the applicator contains a supply of radioactive seeds forimplantation. Typically the radioactive seeds are supplied in the formof a cartridge or magazine, which is mated to the applicator. The numberof seeds supplied by the cartridge or magazine is usually less than thetotal number of seeds needed for the brachytherapy procedure.Accordingly, the applicator may need to be resupplied with seeds severaltimes during the procedure. The seed-holding system and techniquesdescribed below facilitate the rapid resupply of seeds to an applicator.The seed-holding system provides for a holder, which may be disposable,and a transfer device, which may be reusable. The holder stores theradioactive seeds. Several holders loaded with radioactive seeds may beprepared for a single brachytherapy procedure. The transfer device helpsdispense the seeds from the holder, and also provides shielding to theseeds, reducing the risk to medical staff of radiation exposure. Whenthe holder is coupled to the transfer device, the seed-holding systemcan be mated to an applicator, and radioactive seeds may be dispensedfrom the holder. When the holder is emptied of seeds, the seed-holdingsystem may be disconnected from the applicator, and the empty holder maybe ejected from the transfer device. A fresh, full holder may then becoupled to the transfer device, and the seed-holding system may onceagain be mated to the applicator. The implantation of seeds may thencontinue. The resupply of seeds may be completed in a matter of seconds.

In one embodiment, the present invention provides a device, including aholder and a transfer device. The holder, which is configured to receiveone or more radioactive seeds, includes two components: a main body anda pusher. Both parts may be made of plastic. The holder is furtherconfigured to mate to an applicator, and to dispense seeds from theholder's distal end. The transfer device, which is configured to engagethe holder, is composed of several components, including a housing, anexpansive spring and a pusher assembly. The transfer device may furtherinclude a shield that can be extended to provide radiation shieldingaround the holder.

Other advantages, features and embodiments of the invention will becomeapparent from the following detailed description and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a seed-holding device, including aholder and a transfer device.

FIG. 2 is a cutaway view of a radioactive seed holding device, includinga holder and a transfer device.

FIG. 3 is a cutaway view of a transfer device and a holder.

FIG. 4A is a left side view of a main body of a holder.

FIG. 4B is a front view of a main body of a holder.

FIG. 5 is a cross-sectional view of fingerlike projections of a holderengaged to a clamp ring of a transfer device.

FIG. 6A is a front view of a pusher.

FIG. 6B is a front view of the pusher shown in FIG. 6A, with a handle.

FIG. 6C is a front view of another embodiment of a pusher, with ahandle.

FIG. 7 is a cross-sectional view of a seed-holding device mated to anapplicator.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of seed-holding system 10. System 10includes holder 12 and transfer device 46. In FIG. 1, holder 12 andtransfer device 46 are shown coupled.

Holder 12 stores one or more radioactive seeds. When seed-holding system10 is mated to applicator 96 as shown in FIG. 7 and as described in moredetail below, radioactive seeds may be dispensed from holder 12 one at atime though distal end bore 30. After a seed is dispensed, a new seed isforced into a position in which the new seed can be dispensed thoughdistal end bore 30. The force used to move the new seed into position issupplied by expansive spring 94 (see FIG. 2) in transfer device 46.

In one embodiment, holder 12 is constructed of plastic, such asthermoplastic, and may be formed by several processes, such as molding.Thermoplastic construction offers many advantages, including inexpensivemanufacture, disposability, and ease of sterilization. Plastic offers afurther advance of allowing holder 12 to deform when coupling to anduncoupling from transfer device 46, as will be described more fullybelow. In addition, the plastic may be color-coded to identify the typesof seeds contained within. For example, one color may indicate seedsincluding iodine-125, and another color may indicate seeds made ofpalladium-103.

Transfer device 46, in one embodiment, is constructed of metal such asstainless steel, and is reusable. When transfer device 46 is coupled toholder 12 as shown in FIG. 1, seed-holding system 10 can be mated toapplicator 96, and radioactive seeds may be dispensed from holder 12. Asa holder 12 is emptied of seeds, seed-holding system 10 may bedisconnected from applicator 96, and empty holder 12 may be ejected fromtransfer device 46 and discarded. A fresh, full holder 12 may then becoupled to transfer device 46, and seed-holding system 10 may once againbe mated to applicator 96.

FIGS. 2 and 3 are cutaway views showing more details of holder 12 andtransfer device 46. In FIG. 2, holder 12 and transfer device 46 areshown coupled, and in FIG. 3, holder 12 and transfer device 46 are shownseparated.

Holder 12 includes main body 14 and pusher 32, shown cut away in FIGS. 2and 3. Main body 14 defines a sleeve-like cavity 16, which holds aplurality of radioactive seeds 18. Main body 14 and/or pusher 32 can becolor-coded. In addition, main body 14 can be made from a material(e.g., clear plastic) that allows the contents of holder 12 to beviewed. Each radioactive seed 18 is substantially cylindrical. In theembodiment depicted in FIG. 2, sleeve-like cavity 16 holds twentyradioactive seeds 18. (In FIG. 3, seeds 18 have been removed to showsleeve-like cavity 16 more clearly.) Seeds 18 are generally loaded intoholder 12 by sliding seeds 18 laterally into sleeve-like cavity 16 atproximal end 20 of holder 12. Once seeds 18 are loaded into sleeve-likecavity 16, pusher 32 may be inserted into sleeve-like cavity 16 atproximal end 20 of holder 12, where pusher 32 abuts seeds 18. Techniquesfor loading seeds and inserting pusher 32 into sleeve-like cavity 16will be described in more detail below. Seeds may be dispensed end-firstfrom the distal end 22 of holder 12 through distal end bore 30.

Main body 14 of holder 12 is shown in more detail in FIGS. 4A and 4B. Asshown in FIGS. 1, 2, 3, 4A and 4B, main body 14 is substantially planar,but main body 14 may assume a configuration other than planar. The shapeof main body 14 ordinarily may be selected to allow holder 12 to fitinto a slot of seed applicator 96. As shown in FIGS. 3, 4A and 4B, mainbody 14 of holder 12 includes optional proximal disk protrusion 26 andoptional central disk protrusion 28. Disk protrusions 26 and 28 allowholder 12 to couple to transfer device 46, which is substantiallycylindrical, and to prevent holder 12 from wobbling when coupled totransfer device 46. Main body 14 may include optional directionalfeature 106, as depicted in FIGS. 1 and 4B. Directional feature 106 isuseful for keying holder 12 to a particular applicator, permittingcoupling of holder 12 to the applicator in only one direction. Inaddition, holder 12 may optionally include securing feature 112,depicted in FIGS. 1, 4A and 4B as a groove. When seed-holding system 10is inserted in a particular applicator, the applicator may be securelycoupled to holder 12 by gripping securing feature 112. Directionalfeature 106 and securing feature 112 typically depend upon theapplicator to which holder 12 will mate and upon the securing mechanismused by the applicator. Consequently, holders may be created withdifferent conformations, each conformation configured to work with adifferent kind of applicator. Directional feature 106 and securingfeature 112 shown in FIGS. 1, 4A and 4B are merely exemplary, and theinvention is not limited to the features depicted.

As shown in FIGS. 3 and 4B, and as shown in more detail in FIG. 5,proximal end 20 of main body 14 includes two pairs of fingerlikestructures, 42 and 44. As shown in the cross-sectional views of FIGS. 2and 5, holder 12 couples to transfer device 46 by engaging fingerlikestructures 42 with clamp ring 50. Outer pair of fingerlike structures 42are configured to deform to slide over clamp ring 50 and snap intoplace. Outer pair of fingerlike structures 42 are further configured todeform upon application of distally directed pressure, as will bedescribed in more detail below, thereby disengaging from clamp ring 50and uncoupling holder 12 from transfer device 46.

Inner pair of fingerlike structures 44 provide added protection againstaccidental slippage of pusher 32 from sleeve-like cavity 16. If holderis accidentally dropped, for example, inner pair of fingerlikestructures 44 reduce the risk that pusher 32 will be separated from mainbody 14, and thus reduce the risk of seed spillage.

Holder 12 can be loaded with seeds by a manufacturer or by a localmedical staff member. Seeds can be obtained from any source such as acompany specializing in brachytherapy. Typically, such companies provideseeds in bulk. To load holder 12, a person can count the seeds, verifythe seeds' radioactivity, and place the seeds into sleeve-like cavity 16of main body 14. Once loaded, holder 12 can be sterilized by, forexample, autoclaving. Pusher 32 is useful in loading as well as inactual use of device 10.

FIG. 6A shows an embodiment of pusher 32. Pusher 32 includes notch 34that receives distal end 92 of shaft 82 (shown in FIG. 3) of transferdevice 46. Pusher 32 further includes drag structures 38, which allowpusher 32 to slide inside sleeve-like cavity 16 but which also preventpusher 32 from sliding freely. As shown in FIG. 6A, drag structures 38are in the form of side protrusions, with diamond-shaped aperturesproviding spring-like flexibility. Another embodiment of drag structures38 is shown in FIG. 6C, in which drag structures 38 are cantileveredsprings. FIGS. 6B and 6C show an optional temporary handle 36, useful inplacing pusher 32 into sleeve-like cavity 16. When staff load main body14 with seeds, pusher 32 can be used as a tamp to assure the seeds areproperly seated in sleeve-like cavity 16. Temporary handle 36 allowspusher to be easily inserted into sleeve-like cavity 16 and to be easilywithdrawn. Temporary handle 36 is coupled to pusher 32 by snap-offconnection 114. Once main body 14 is loaded and pusher 32 is insertedinto sleeve-like cavity 16 and placed in contact with stack of seeds 18,temporary handle 36 can be snapped off and discarded. If it is laternecessary to remove pusher 32 from sleeve-like cavity 16, a tool may beused to grab removal features 40 of pusher 32 and extract pusher 32.Removal features 40 may be structures such as protrusions, indentationsor apertures. Drag structures 38, temporary handle 36 and removalfeatures 40 may be integrally formed with pusher 32 during the formationprocess.

Transfer device 46 can contain metal (e.g., stainless steel) to provideradiation shielding. It will be understood that transfer device 46 canbe made of other materials as well (e.g., molded plastic). In additionto providing radiation shielding, metal construction provides advantagessuch as increased durability and ease of sterilization. As shown inFIGS. 1, 2 and 3, transfer device 46 includes housing 48. Housing 48need not be substantially cylindrical as shown in FIGS. 1, 2 and 3, butcylindrical configuration allows housing to flexibly couple to differentconformations of holders 12. When housing 48 is substantiallycylindrical, transfer device 46 can have an outer shape that preventsthe transfer device 46 from rolling across a flat surface (e.g., atable). For example, transfer device 46 can have a flat boss (not shown)to prevent rolling.

Because housing 48 is the component of transfer device 46 that is mostlikely to be touched and handled, exterior surface 68 of housing 48 maybe coated or textured to make housing 48 easier to grasp. In theembodiment depicted in FIGS. 1, 2 and 3, housing 48 is a cylindricallyshaped casing coupled to proximal end cap 60 and distal end cap 62.These components may be produced in many ways, such as from rod andtubing stock by machining, and may be joined in several ways, such as bythreads, interference press fit or adhesive bonding. Housing 48 may beformed in other ways, such as by joining complementary molded halves.Housing 48 encases clamp ring 50, which is held in a fixed positionrelative to housing 48. Clamp ring 50 may be a separate component joinedto housing 48, or may be formed integrally with housing 48. In oneembodiment, housing 48, proximal end cap 60, distal end cap 62, andclamp ring 50 are formed integrally as two identical halves that can bejoined together. For example, housing 48, proximal end cap 60, distalend cap 62, and clamp ring 50 can be made of two identical moldedplastic pieces that are joined together to form a single unit.

When housing 48 is made of plastic, a first metal inner lining (notshown) can be fitted inside housing 48. The first inner lining can befitted inside housing 48 such that the first metal inner lining extendsfrom proximal end cap 60 to clamp ring 50. Likewise, a second metalinner lining (not shown) can be fitted inside housing 48 such that, forexample, the second metal inner lining extends from clamp ring 50 todistal end cap 62. Typically, the first and second metal inner liningshave a shape corresponding to the inner shape defined by housing 48. Forexample, if housing 48 defines an inner shape that is cylindrical, thenthe first and second metal inner linings can be cylindrical. Typically,the first and second metal inner linings are designed to provideradiation shielding. Any method can be used to make transfer device 46fitted with first and second metal inner linings within housing 46. Forexample, the first and second metal inner linings can be hollow metaltubes. Such hollow metal tubes can be fitted within two identical halvesof molded plastic that can be joined together. Once joined together, thetwo identical halves of molded plastic can define housing 48, proximalend cap 60, distal end cap 62, and clamp ring 50.

When housing 48 is made of plastic, a metal outer lining (not shown) canbe fitted outside housing 48. The metal outer lining can be fittedoutside housing 48 such that the metal outer lining extends fromproximal end cap 60 to distal end cap 62. Typically, the metal outerlinings have a shape corresponding to the outer shape defined by housing48. For example, if housing 48 defines an outer shape that iscylindrical, then the metal outer lining can be cylindrical. Typically,the metal outer lining is designed to provide radiation shielding. Inone embodiment, housing 48 can be fitted with a metal inner lining and ametal outer lining. For example, housing 48 can be fitted with a metalinner lining that extends from proximal end cap 60 to clamp ring 50 anda metal outer lining that extends from clamp ring 50 to distal end cap62.

Distal end cap 62 defines distal end opening 66, through which shield 70extends and retracts. Shield 70 is substantially cylindrical, with anouter diameter slightly smaller than the inner diameter of housing 48,allowing shield 70 to extend and withdraw. Flange 74 on shield 70prevents shield 70 from slipping through distal end opening 66. Althoughshield 70 may be spring-loaded or otherwise biased to assume an extendedposition, shield 70 may also deploy by gravity. Shield 70 is shown inFIG. 1 in a partially retracted position, and is shown in FIGS. 2 and 3in a fully extended position. When extended, shield 70 covers holder 12and the seeds 18 within holder 12, thus providing enhanced radiationshielding.

Proximal end 56 of housing 48 is enclosed, except for opening 64 inproximal end cap 60, through which shaft 82 of pusher assembly 54slides. As shown in FIGS. 2 and 3, pusher assembly 54 includes push disk80, which is external to housing 48. As will be described below, pushdisk 80 is used to eject holder 12 from transfer device 46. Push disk 80is affixed to shaft 82. Shaft 82 includes upper portion 84 and lowerportion 86. Upper portion 84 extends from push disk 80 through proximalend opening 64 to spring plate 88. Lower portion 86 of shaft 82 extendsfrom spring plate 88 toward distal end 58 of transfer device 46. Pushdisk 80, upper portion 84 and lower portion 86 of shaft 82 and springplate 88 may be formed from separate components and joined together, ormay be formed as an integral unit. In addition, push disk 80, upperportion 84 and lower portion 86 of shaft 82 and spring plate 88 can bemade of any material (e.g., metal or plastic). A metal construction canprovide radiation shielding. For example, when housing 48, proximal endcap 60, distal end cap 62, and clamp ring 50 are formed integrally asmolded plastic, first and second metal inner linings and a spring plate88 made of metal can be used to provide radiation shielding.

When fully-loaded holder 12 is inserted into transfer device 46, distalend 92 of shaft 58 engages notch 34 of pusher 32. As holder 12 isinserted farther into transfer device 46, expansive spring 94 iscompressed and upper portion 84 of shaft 82 is pushed further outside ofhousing 48. When fingerlike structures 42 engage clamp ring 50, upperportion 84 of shaft 82 is fully extended outside housing 48. As seedsare dispensed from seed-holding system 10, upper portion 84 descendsincrementally into housing 48. When all seeds are dispensed, most ofupper portion 84 is inside housing 48. Consequently, the percentage ofupper portion 84 that is outside housing 48 at any particular time, andtherefore visible to the user of device 10, is a function of the numberof seeds in holder 12. Graduated marks 90 placed on upper portion 84 ofshaft 82 may be used to provide visual feedback of the number of seedsremaining in holder 12. Graduated marks 90 may be, for example, etchedinto the metal or painted on upper portion 84.

Transfer device 46 provides spring-loading for seeds 18 in holder 12.Expansive spring 94 (shown in FIG. 2 but omitted from other figures forclarity) is located between spring plate 88 and proximal end cap 60.Spring 94 drives spring plate 88 away from proximal end 56 of housing48. When a fully-loaded holder 12 is inserted into transfer device 46and fingerlike structures 42 engage clamp ring 50, spring 94 is placedin compression as shown in FIG. 2. As spring 94 exerts force againstspring plate 88, lower portion 86 of shaft 82, which is coupled tospring plate 88, exerts force against pusher 32. Pusher 32 in turnexerts force against seeds 18. As a seed is dispensed through distal endbore 30, spring 94 causes shaft 82 to move incrementally into towarddistal end 58 of housing 48, causing pusher 32 to push remaining seeds18 distally, thereby aligning a new seed with distal end bore 30.

FIG. 7 shows seed-holding system 10 mated to an exemplary applicator 96.Applicator 96 may be one of many instruments used in brachytherapyprocedures, such as a Mick applicator. The opening in applicator 96 thatreceives device 10 causes shield 70 to retract while allowing distal endbore 30 of holder 12 to align with applicator bore 98. In a typicalapplicator, a push rod (not shown) slides back and forth throughapplicator bore 98 to push seeds through applicator bore 98 into animplantation needle (not shown). When seed-holding system 10 is mated toapplicator 96, the push rod can slide through distal end bore 30,thereby pushing a seed end-first out of holder 12 and into applicatorbore 98. After the seed is dispensed and the push rod withdrawn, spring94 drives shaft 82 and pusher 32 distally, bringing a new seed inposition in distal end bore 30, ready to be dispensed.

As shown in FIG. 7, seed-holding system 10 is empty. In this state, apush rod is prevented from extending through holder 12 because the pushrod's path through distal end bore 30 is obstructed by pusher 32. Theseed holding system 10 is ready to be disengaged from applicator 96.Once seed-holding system 10 is disengaged from applicator 96, emptyholder 12 is ejected by holding housing 48 of transfer device 46, andpushing on push disk 80. Pushing on push disk 80 drives pusher assembly54 distally, which drives pusher 32 against distal end bore 30. Pusher32 is at the end of sleeve-like cavity 16 and cannot advance further. Asa result, pressure on push disk 80 overcomes the engagement of outerfingerlike structures 42 with clamp ring 50. Outer fingerlike structures42 deform and disengage from clamp ring 50, allowing holder 12 to beeasily removed from transfer device 46.

A number of embodiments of the present invention have been described.Nevertheless, various modifications may be made without departing fromthe spirit and scope of the inventions as set forth in the claims thatfollow. For example, seed-holding system 10 may hold spacers in additionto radioactive seeds. Spacers are non-radioactive objects usuallysimilar in size to radioactive seeds. Spacers interspersed betweenradioactive seeds are useful in placing radioactive seeds at desireddepths within tissue.

What is claimed is:
 1. A device comprising: a holder configured toreceive at least one radioactive seed, comprising a main body and apusher that slides in the main body; a transfer device configured toengage the holder, the transfer device defining a proximal end and adistal end and comprising a housing, an expansive spring and a pusherassembly, the pusher assembly configured to engage the pusher, and theexpansive spring configured to drive the pusher assembly toward thedistal end of the transfer device.
 2. The device of claim 1 wherein theholder is configured to couple to a seed applicator.
 3. The device ofclaim 1 wherein the main body defines a proximal end and a distal end,and wherein the proximal end of the holder is configured to receive theradioactive seed.
 4. The device of claim 1 wherein the main body definesa proximal end and a distal end, and wherein the distal end of theholder is configured to dispense the seed.
 5. The device of claim 1,wherein the transfer device comprises a shield configured to extend fromthe distal end of the transfer device.
 6. The device of claim 5, whereinthe shield is movable by spring force.
 7. The device of claim 5, whereinthe shield is movable by gravity force.
 8. The device of claim 1,wherein the main body and pusher are made of thermoplastic.
 9. Thedevice of claim 1, wherein at least a portion of the main body iscolor-coded.
 10. The device of claim 1, wherein the contents of theholder are viewable through the material of at least a portion of themain body.
 11. The device of claim 1, wherein the transfer devicecomprises metal.
 12. The device of claim 11, wherein the transfer deviceis made of stainless steel.
 13. The device of claim 1, wherein thetransfer device comprises metal and plastic.
 14. The device of claim 1,wherein the distal end defines a distal end bore, and wherein the pusherobstructs the distal end bore in the absence of radioactive seeds.